ABSTRACT Liver fibrosis is an abnormal healing response to chronic liver injury and predisposes patients to cirrhosis, which is a major cause of death worldwide. Although fibrosis has many etiologies, it only occurs after portal fibroblasts and or hepatic stellate cells (HSCs) differentiate into myofibroblasts, a process termed activation. HSCs are the major contributors to the myofibroblast population in fibrosis and chronic liver damage stimulates continuous HSC activation, tissue contraction and excessive extracellular matrix (ECM) deposition, resulting in fibrosis and organ failure. Thus, it is important to understand the factors that contribute to fibrosis progression and HSC myofibroblast differentiation, such as the physical microenvironment. To date, in vitro studies have shown that substrate elasticity is a critical mediator of myofibroblast differentiation, using hydrogels of varied mechanics. This is thought to mimic the changes in liver stiffness that occurs during fibrosis; however, cells in the liver reside in a fibrous 3D ECM, which may not be recapitulated with seeding atop smooth hydrogels. Importantly, fibrous materials may be manipulated by cells and have non-linear mechanics that enable long- range force transmission through fiber alignment. Thus, the objective of this proposal is to develop tunable synthetic fibrous materials based on hyaluronic acid that mimic the ECM of the liver to investigate how static and dynamic fiber mechanics influence HSC activation and migration. These proposed fibrous systems are unique from both natural ECMs that are difficult to tailor and from typically rigid synthetic fibers. The first Aim of this proposal will be the development of nanofiber cell culture substrates with a range of mechanical properties. It is hypothesized that stiffer nanofibers will limit cell fiber remodeling and activation, while softer nanofibers will permit fiber remodeling/recruitment and activation under the fibrogenic stimulus TGFb1. Aim 2 of this proposal will be the development of nanofibrous materials that can be locally stiffened around HSCs using light triggered chemical reactions to mimic the dynamic crosslinking of ECM that occurs during fibrosis. It is hypothesized that HSCs will migrate directionally based on local fiber mechanical properties. Together, the materials developed here will provide new platforms to study fibrosis and healing, inspire the development of new fibrosis therapies, and provide training within new materials and HSC biology to the applicant.